1. Field of the Invention
This invention relates to systems for treating liquid solutions to remove dissolved heavy metals. More particularly, the invention relates to removing heavy metal ions and complex heavy metal ions from potable and municipal, commercial and industrial waters as well as from commercial and industrial non-aqueous waste solutions, especially in the presence of lighter metal ions commonly found in water such as calcium, magnesium and sodium ions.
2. Brief Description of the Prior Art
The initial motivation to develop such a system resulted from publicity on the adverse effect of lead in drinking water. By the late 1980's, the scientific date documented the diminished IQ performance in children with sub-clinical (asymptomatic) lead intoxication levels. This resulted in passage by the U.S. congress of the Lead Contamination Control Act of 1988. This Act targeted water supplies in the nation's schools, followed by public water systems. The Act is consistent with the national effort to remove lead from gasoline, and paint, and now water. In recent years, this effort has been extended to the control of levels of other metal contaminants, such as cadmium, mercury and other metals often found in drinking water. On the other end of the water-use spectrum, government regulations are closing in on the concentration and total amount of heavy metals allowed in municipal, commercial and industrial waste streams which reenter the environment. The tendency in regulation of industrial waste water is toward a goal of "drinking water in, drinking water out".
Workers in the field of high performance affinity liquid chromatography (HPLC) have, in recent years, developed silica packing materials for purifying mixtures produced in the biotechnology and pharmaceutical sciences. These silica packing materials exhibited high physical integrity and low non-specific binding of dissolved organic material when used for the purposes intended in high performance affinity liquid chromatography. Therefore, it seemed that use of such material for purifying potable and waste water streams might be possible. However, upon further inspection, it was realized that such chromatographic silica packing materials were susceptible to permitting the leaching of solid compounds containing the heavy metals that were bound, resulting in fouling or plugging the packing materials and release of the metals to the environment. Consequently, the leaching effects made such silica packing materials unsuitable for potable or waste water treatment applications.